Outboard clicking/knocking noise problem

[Neil_Y]

A friend has a 10hp Honda 4stroke outboard in his yacht (this is Swedish and mounted like a sail drive through the hull) He can't access the leg once launched as it's sealed through a large hole like a saildrive.

Just before it was hauled out it started clicking/knocking metallic sound once every 2 or 3 seconds it seemed connected with rpm but I can't think of anything that would rotate that slowly.

He has to launch at the end of the week and has asked me to go and have a look, which might mean a leg strip down I'm guessing.

has anyone else had or come across anything similar in terms of noise and frequency with an outboard? to help guide me on where to look first.

Thanks for the help

 

[Stemar]

A faint ticking coupled with rough running on my Tohatsu 3.5 2T turned out to be sparking due to corrosion in the HT earth from the coil, cured by a general cleanup of the connection.

 

[VicS]

A friend has a 10hp Honda 4stroke outboard in his yacht (this is Swedish and mounted like a sail drive through the hull) He can't access the leg once launched as it's sealed through a large hole like a saildrive.

Just before it was hauled out it started clicking/knocking metallic sound once every 2 or 3 seconds it seemed connected with rpm but I can't think of anything that would rotate that slowly.

He has to launch at the end of the week and has asked me to go and have a look, which might mean a leg strip down I'm guessing.

has anyone else had or come across anything similar in terms of noise and frequency with an outboard? to help guide me on where to look first.

Thanks for the help

It could be a misfire on one cylinder, perhaps for a similar reason to Steve's suggestion.

What was done/ checked during its last service, presumably done during the winter?

 

[Neil_Y]

Thanks, I'll check for sparks where they shouldn't be but he said it was running OK, no misfire.

He's done a leg oil change, but that's all and it started making the noise as he drove it to the lift out at the end of last season.

He said ticking frequency was once every 2 or 3 seconds which is what confused me, assuming at idle it's doing 800-1000rpm I think I'll go to see it this evening so may have more information later. But only a week to sort it before planned lift in.

The system is one of these which are quite common in Sweden http://www.saildrive.se/

 

[Appledore]

My Tohatsu 3.5 2-stroke outboard started making a knocking noise last year. Was fine out of gear, but kept knocking once under way. Turned out to be caused by a badly corroded impellor housing (actually cracked). I found it difficult to believe this would cause the noise, but after the guy replaced the housing and impellor it stopped, and has been fine since.

 

[Neil_Y]

Thanks Appledore,
I'll take a close look at the leg castings, we'll probably strip the leg and bottom gear.

 

[Neil_Y]

Looked at engine last night, and the only thing I can think of that might reciprocate or rotate that slowly is the fuel pump? does that make sense to anyone.

The ticking is definitely once a second at engine idle speed, we checked the belt camshaft drive, and the starter clutch/teeth/springs and it all looks good.

Trouble is even though it's an outboard it's installed as an inboard so we can't just lift it out and take it to a mechanic.

 

[VicS]

Looked at engine last night, and the only thing I can think of that might reciprocate or rotate that slowly is the fuel pump? does that make sense to anyone.

The ticking is definitely once a second at engine idle speed, we checked the belt camshaft drive, and the starter clutch/teeth/springs and it all looks good.

Trouble is even though it's an outboard it's installed as an inboard so we can't just lift it out and take it to a mechanic.

Can you locate the area from which the noise is coming using a " listening stick" or an engineer's stethoscope ?

 

[Neil_Y]

Tried that, it wasn't that helpful the noise was the same so it doesn't seem to be internal, so an external noise seems to be something possibly catching the cam belt, but probably under the starter where you can't see to much.

John Bower from SMS in Salcombe/Plymouth was helpful in confirming there is nothing rotating or reciprocating at that sort of speed. The fuel pump operates on a cam at half engine speed and the tick is = to 60rpm not 400. I was thinking fuel pump as it sounds like a broken spring ticking/catching. Last resort seems to be a strip down at the weekend, but it's only accessible by climbing into the cockpit locker as it's under the cockpit floor, one of those awkward boat jobs.

 

[anoccasionalyachtsman]

Is it connected electrically - as in charging circuits? Just wondering if there's a relay nearby doing something that it probably shouldn't?

 

[oldharry]

"ticking every 2 to 3 seconds". Does that mean it's not a regular noise? If so it's not something rotating in the engine. It's unlikely anyway as at 800 rpm the engine will have rotated up to 2400 times, and it's unlikely anything is geared that low. If it is an irregular noise happening every 2 or 3 seconds then it's more likely something is loose, or an intermittent ht arcing as suggested. You need to try añd locate where the noise is before pulling everything to pieces.

 

[Neil_Y]

Solved or at least found the problem.

The problem was teeth missing on the drive bevel gear on the drive shaft coinciding with a couple of teeth missing on one of the large forward bevel drive gears.

The noise being much slower than the engine speed was because it only slipped when the missing teeth on the drive bevel and the prop shaft bevel coincided! so at 800rpm we had a 60rpm ticking noise. Now I find out that original Honda gears in Sweden are £200 each! £400 for parts and a few hours putting it back together.
But thanks for the suggestions and help.

 

[Neil_Y]

800rpm is only 13.33 rev per second. We were getting ticking noise every second at that engine speed, so every 13 or 14 revolutions of drive shaft matched all the broken teeth together. Interesting problem, as it really sounded as if it was outside of the engine so we were thinking fuel pump or can drive belt which runs at half engine rpm.

 

[VicS]

Solved or at least found the problem.

The problem was teeth missing on the drive bevel gear on the drive shaft coinciding with a couple of teeth missing on one of the large forward bevel drive gears.

The noise being much slower than the engine speed was because it only slipped when the missing teeth on the drive bevel and the prop shaft bevel coincided! so at 800rpm we had a 60rpm ticking noise. Now I find out that original Honda gears in Sweden are £200 each! £400 for parts and a few hours putting it back together.
But thanks for the suggestions and help.

Thanks for letting us know the reason

I wonder what had caused the damage to the gears

 

[anoccasionalyachtsman]

I'm annoyed that I didn't think of that. The current gearbox in my ageing Land Rover has a couple of broken teeth and does just the same! (I've just rebuilt a replacement).

 

[Hadenough]

Had the same problem with the bevel drive gears on my Lambtreta LD125 in 1968/9ish. Couldn't afford to repair it so went to work each day like a Kangaroo.

 

[Neil_Y]

I'm annoyed that I didn't think of that. The current gearbox in my ageing Land Rover has a couple of broken teeth and does just the same! (I've just rebuilt a replacement).

Me too in a way, I was convinced it was outside the engine from the clarity of the clicking. I've done the maths now and the number of teeth on the two bevel gears 13 and 28 mean that it moves on two teeth every rev of the engine, and then meets the bad one every 14 revolutions. 800rpm = 13.3 rpm which = the one second click

 

[oldharry]

+1. I had an old BSA A10 doing exactly the same due to missing teeth - excuse is it was a long time ago! Sold that machine for £20. Sigh.

Yes Vic is of course right 800 revs per minute is 13.3 revs per second - still massive downgearing which of course is exactly what Neil found. Thanks for letting us know Neil